The field of this invention is a.c. generators which are driven by a gasoline or diesel engine and more particularly to a control circuit for an a.c. generator such as that disclosed in U.S. Pat. No. 3,656,051 entitled "Fast Response Feedback Controlled Generator".
In an a.c. generator such as is disclosed in the above-cited patent, the generator output voltage is controlled by regulating the current in the generator field winding. A current control circuit, which physically rotates with the generator shaft, is responsive to feedback signals, varying in accordance with the generator output signal, the feedback signals being supplied to the current control circuit from a stationary feedback circuit through a rotating transformer or an optical transceiver. By regulating the a.c. generator field current in accordance with the a.c. generator output voltage, the current control circuit maintains a constant generator output voltage.
While great care is taken in the design of electronic control circuits and in particular the electronic control circuits for an a.c. generator, it is inevitable that one or more components will occasionally fail. To the extent possible, such control circuitry should be designed so that when a component failure occurs, the electronic circuit fails in a safe mode. In the case of an a.c. generator such as is disclosed in the above cited patent, it is desirable that the output voltage of the a.c. generator drop to a safe level when a component failure in either of the feedback circuit or the current control circuit occurs.